Proposals have already been made, in French patent application No. 94 00539 (published under No. 2 715 244) for lightweight noise-absorption structures each comprising a support frame on which a gastight membrane is fixed and tensioned, together with plates disposed beneath the membrane to co-operate therewith to form a passive laminar air-flow damper. Soundwaves incident on the side of the membrane remote from said plates give rise to vibratory deformation of the membrane which in turn gives rise to a laminar flow of air between the membrane and the plates, and thus to energy being absorbed. When the acoustic impedance of such a structure is properly matched to the incident soundwaves, a large portion of the energy of said soundwaves is absorbed by the structure over a relatively broad frequency band.